Review Index:

Intel Core i5-661 Clarkdale Processor Review - Westmere debuts

Subject: Processors
Manufacturer: Intel

Westmere meets the desktop


2009 has been a mixed blessing for Intel in many ways.  Even though from a processor technology stand point the company has dominated the once-competitive AMD Athlon and Phenom brands with the release of the Nehalem architecture back in November of 2008, the business side of the company has seen blow after blow after blow.   In May the EU fined Intel for $1.45 billion (with a 'b') for antitrust violations, Intel and AMD settled a civil dispute that resulted in Intel writing a $1.25 billion (also with a 'b') check to AMD and most recently Intel was sued by the US FTC for anti-competitive practices.  Yeoch. 

Oh, and Larrabee was canceled

But despite all of that, where the meat and potatoes of the company is focused in terms of processors, Intel continues to be very successful.  The Nehalem launch for the high-end desktop market went well though likely saw fewer sales than hoped but the Lynnfield product was even better offering similar levels of performance for a lower price to both consumers and system integrators. 
Today Intel is releasing the next iteration of the Nehalem architecture for an even lower price segment that includes some slight technological advancements to boot. 

Westmere Architecture

In reality, what we know as Westmere does not differ all that much from Nehalem (both Bloomfield and Lynnfield).  Both are built on nearly identical compute architectures with the major changes being in features and core counts and of course a transition from 45nm technology to the latest from Intel's fabs, 32nm High-K. 

The major additions to the Nehalem core?  Dramatic changes in the architecture noted above, the return of HyperThreading as an optional performance improvement, an integrated memory controller (no longer on the chipset), a new cache structure, the removal of the front-side bus bottleneck and of course much improved control over the power consumption of the CPU.

Along with that new power controller Intel introduced Turbo Mode:

Perhaps the most interesting bit of news out of Intel's Nehalem was something called Turbo Mode - a feature directly enabled by the PCU we discussed on the previous page.  With modern processors, the debate has raged whether users are better off getting a quad-core CPU at a lower frequency or a dual-core CPU at a higher frequency.  Intel is hoping that with Turbo Mode users will get the best of both worlds.

The idea is pretty straight forward: if you have four cores that run at combined power consumption (and heat dissipation) of X, then if you only have two cores loaded (with the other two at idle) then you have additional power headroom to overclock the working cores to a higher frequency.

There are some very notable changes however to the Westmere core, starting with the move to a 32nm process technology.  While this doesn't inherently improve anything for customers it can help Intel lower power consumption and increase clock speeds and of course, lower the cost to produce the chips if yields are predictable.  But apparently with this transition there were some interesting consequences that we'll discuss below.
Westmere does see the addition of a new set of instructions meant to accelerate AES encryption and decryption.  Applications like WinZIP that currently use AES standards will see some dramatic performance increases and future whole-disk encryption algorithms will likely be accelerated as well.

The first Westmere parts, Clarkdale for the desktop and Arrandale for the mobile, will both be dual-core only parts.  We will go over all the specific product announcements later in the review. 

A Little Side Project

The integrated memory controller that was one of the big architectural
changes from the Core 2 product line has been removed from the Westmere CPU core
and placed on a separate chip on the same substrate.  This second chip
also includes integrated graphics and the PCI Express lanes necessary
for communicating with the rest of the system. 

Interestingly, this chip is built on the current 45nm process technology rather than the newer 32nm technology for the Westmere core.  The image above is to scale: the 32nm Westmere core on the right has 383 million transistors while the 45nm memory controller and graphics die contains only 177 million transistors.  Die sizes are 81 mm^2 and 114 mm^2 respectively. 

The fact that Intel moved the IMC and PCI Express off of the Westmere die leads some on the media to wonder if Intel had issues bringing those segments down to the 32nm transistors that the rest of the Westmere architecture is using.  It is also possible that Intel made the decision to benefit the newly integrated graphics since having the memory controller "one step" closer to it would be more beneficial in terms of performance than having it "one step" closer to the processing cores. 

Later in the article we will evaluate how this migration of the IMC affects CPU and memory performance but for now, let's take a closer look at the new Intel HD Graphics core.